1. Field of the Invention
The invention relates to the production of diethyl phosphite of high purity and low acidity.
2. Relevant Prior Art
Diethyl phosphite is useful as an intermediate in the production of organophosphorous compounds such as flame retardant compounds and as stabilizers for plastics.
U.S. Pat. No. 2,834,797 discloses a method of producing dialkyl phosphites by the reaction of trialkyl phosphites with molten phosphorous acid. The cited patent teaches reacting a trialkyl phosphite with phosphorous acid in a molar ratio of phosphite to phosphorous acid of about 1:2 to 3:1 and preferably 2:1 for maximum dialkyl phosphite yields. The diethyl phosphite prepared as disclosed in the cited patent is said to result in a 78% of theory yield after distillation, based on triethyl phosphite. Additionally, the dialkyl phosphite product produced in accordance with the process of the cited art has been found to have an acid value in excess of 20.2 milligrams KOH per gram, which for certain applications utilizing diethyl phosphite (for instance, in producing aminoalkyl phosphonates used as fire retardants in urethane foams) would reduce the product yield and additionally would decrease the product purity and prevent it from meeting acidity specification. In such applications an acid value of less than 10 mg of KOH per gm of product is desirable. However, an acid value of less than 5 mg of KOH per gram is preferred.
An object of the invention is to produce a diethyl phosphite product of high purity, having low acidity in high yields without requiring further distillation.